1. Field of the Invention
The present invention relates to an encapsulated measuring device for detecting the velocity and/or acceleration of a rotationally or linearly moved component, in particular for detecting the position and acceleration (velocity) of a rotationally or linearly moved component.
2. Description of the Related Art
Encapsulated photoelectrical linear measuring devices are known from the publication “Digitale Längen-und Winkelmess-technik: Positionsmesssysteme für den Maschinenbau und die Elektronikindustrie” [Digital Linear and Angular Measurement Technology: Position Measuring Systems for Mechanical Engineering and the Electronic Industry] (Moderne Industrie, publ., 4th ed., 2001), pages 48 to 54, which includes of a glass scale and a scanning head, which has a semiconductor light source, a condenser lens, a scanning plate and photo diodes and is arranged on a scanning carriage, which is supported by ball bearings on the glass scale. The scale and the scanning head are arranged protected in an aluminum housing, which has a slit, open at the bottom and closed by elastic sealing lips, so that no foreign objects can penetrate the interior of the aluminum housing. The housing is fastened, for example, on the machine bed of a machine tool, and the tool carriage is connected to a mounting foot, which extends through the sealing lips into the interior of the aluminum housing with an arm in the shape of a sword and takes along the scanning carriage free of play.
Encapsulated angle measuring devices with a photoelectrically scanned graduation on a glass plate, which is fastened on a shaft, are known from the same publication. The graduation and the optical system for scanning the graduation are protected against foreign objects by a sealed housing.
Both systems are used for the highly accurate detection of the position, or angular position, of linearly or rotationally moved components, even under difficult employment conditions.
In connection with the establishment of a high-quality position or velocity control of a rotory or linear electrical drive mechanism it is known from DE 198 51 003 A1 to regulate the acceleration of a moved component directly in an underlayed manner instead of by secondary current regulation. Although it is possible in principle to form the acceleration of a moved component by double differentiation of a detected position signal, a directly measured acceleration is preferred, since with double differentiation of the position signal small detection errors in the position signal are amplified, so that this method is prone to errors. However, it is possible by a directly measured acceleration to produce an optimal regulation structure, wherein a Ferraris sensor is employed as the direct acceleration measuring device which, with rotory drive mechanisms, detects the rotary acceleration of a rotor and, with linear drive mechanisms, the linear acceleration of a rotor.
An analog sensor operating in accordance with the Ferraris principle is known from DE 44 39 233 A1 for detecting the rotary acceleration of a rotationally moved component, which has a rotary body in the form of a disk or of a hollow cylinder made of an electrically conductive non-ferromagnetic material, through one half of which a stationary d.c. magnetic field extends in one direction, and through the other half of which it extends in the other direction. The analog sensor furthermore has a signal detection system with at least one magnetic flux sensor, through which the magnetic flux linked with the eddy currents flowing in the rotary body extends and which has a coil, in which a change of the magnetic flux creates an electrical voltage.
While for detecting the acceleration of a rotationally moved body by an acceleration sensor operating in accordance with the Ferraris system a rotating body is employed as the eddy current body, a Ferraris sensor including a flat eddy current sheet metal plate made of an electrically conductive material and having one scanning head arranged on one side of the eddy current sheet metal plate, or two scanning heads arranged on both sides of the eddy current sheet metal plate, is employed for detecting the acceleration of a linearly moved body. Thus, an eddy current body in the form of a rotating body or eddy current sheet metal plate is required for detecting the acceleration of a rotationally moved component, as well as for detecting the acceleration of a linearly moved component by an acceleration sensor operating in accordance with the Ferraris principle.
However, problems in connection with the arrangement of the various scanning units within the spatially restricted measuring device housing occur in particular with an encapsulated measuring device for detecting the position or angular position of a linearly or rotationally moved component, wherein it is additionally necessary to take into consideration that ball bearing-supported guide elements and couplings must be provided between the scanning carriage connected with the moved component and the measuring device housing, or the fixed scale.
A further problem lies in that with an acceleration sensor operating in accordance with the Ferraris principle it is necessary to arrange the eddy current body at only a slight distance from the scanning head, so that great demands are made on the manufacturing accuracy in connection with measuring devices for linearly moved components, as well as measuring devices for rotationally moved components.